01 - Place the watermelon cubes, cucumber slices, mint leaves, and lime juice in a blender.
02 - Blend until smooth.
03 - Strain the mixture through a fine mesh sieve into a pitcher to remove pulp, if desired.
04 - Add the sweetener, if using, and stir until dissolved.
05 - Pour in the cold sparkling water, gently stirring to combine.
06 - Serve immediately over ice, garnishing with extra mint leaves and a wedge of lime, if desired.